1) Your thumbs shouldn't be crossed over each other like that, lay the thumb of your left hand flat against the grip lower than the other thumb.
2) Don't squeeze the gun with the tips of your right hand fingers. Try the squeeze the gun against your palm with the middle of your fingers. While holding the gun firmly with your right hand, someone should be able to easily pull the tips of your fingers away from the grip.
3) Make sure you're using the pad on the end of your finger, in between the tip and the first knuckle, to pull the trigger. Make sure you pull the trigger straight back toward your palm.